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Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. The stratosphere is situated between about 10 km (6 miles) and 50 km (31 miles) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 miles) altitude. Temperature The stratosphere is layered in temperature because it is heated from above by absorption of ultraviolet radiation from the Sun. Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 26.6°F), just slightly below the freezing point of water.Seinfeld, J. H., and S. N. Pandis, (2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey This top is called the stratopause, above which temperature again decreases with height. The vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The heating is caused by an ozone layer that absorbs solar ultraviolet radiation, heating the upper layers of the stratosphere. The base of the stratosphere occurs where heating by conduction from above and heating by convection from below (through the troposphere) balance out; hence, the stratosphere begins at lower altitudes near the poles due to the lower ground temperature Aircraft flight Commercial airliners typically cruise at an altitude near 10 km in temperate latitudes, in the lower reaches of the stratosphere. They do this to optimize jet engine fuel burn, mostly thanks to the low temperatures encountered near the tropopause. It also allows them to stay above any hard weather, and avoid atmospheric turbulence from the convection in the troposphere. Turbulence experienced in the cruise phase of flight is often caused by convective overshoot from the troposphere below. Although a few gliders have achieved great altitudes in the powerful thermals in thunderstorms, this is dangerous. Most high altitude flights by gliders use lee waves from mountain ranges and were used to set the current record of 15,447m (50,671 feet). Circulation and mixing The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly than vertical mixing. An interesting feature of stratospheric circulation is the quasi-Biennial Oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers such as ozone or water vapor. In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere. See also * Léon Teisserenc de Bort (the discoverer of the stratosphere) * Paris Gun (first artificial object to reach stratosphere) * SR-71 Blackbird * Concorde * Lockheed U-2 * RQ-4 Global Hawk * Twinjets service ceiling * Le Grand Saut References External links af:Stratosfeer ar:ستراتوسفير bs:Stratosfera ca:Estratosfera cs:Stratosféra da:Stratosfære de:Stratosphäre el:Στρατόσφαιρα es:Estratosfera eo:Stratosfero eu:Estratosfera fr:Stratosphère gl:Estratosfera ko:성층권 hr:Stratosfera id:Stratosfer it:Stratosfera he:סטרטוספירה ka:სტრატოსფერო lv:Stratosfēra lt:Stratosfera hu:Sztratoszféra mk:Стратосфера nl:Stratosfeer ja:成層圏 no:Stratosfæren nn:Stratosfæren pl:Stratosfera pt:Estratosfera ru:Стратосфера sk:Stratosféra sr:Стратосфера fi:Stratosfääri sv:Stratosfär th:สตราโทสเฟียร์ vi:Tầng bình lưu tr:Stratosfer uk:Стратосфера wo:Yolom-jawwu zh:平流层 Category:Atmosphere Category:Meteorology